Dartmouth Engineer - The Magazine of Thayer School of EngineeringDartmouth Engineer - The Magazine of Thayer School of Engineering

What About Nuclear?

Two Thayer professors weigh in on safety and need.

Interviews by Adrienne Mongan

Professor Graham Wallis:

SAFEGUARDING NUCLEAR ENERGY

Thayer School’s Sherman Fairchild Professor of Engineering, Emeritus, Graham Wallis served on the Advisory Committee on Reactor Safeguards (ACRS) of the Nuclear Regulatory Commission (NRC) from 1998 to 2007. The NRC oversees safety, licensing, and waste management for nuclear reactors.

Nuclear reactor Can nuclear reactors be made safer?
The safety standards and regulations established by the NRC are quite stringent, and all nuclear reactors must comply with them. The new reactors that are coming before the NRC have been designed with improved safety features. For example, new reactors require less human intervention during an accident, which will possibly reduce the amount of human error, though trained operators may still take appropriate action when necessary. The new reactors are designed to have passive emergency coolant systems relying on gravity, so pumps do not have to function following an accident to ensure that the reactor temperature does not rise above a level which could damage the fuel and release radioactive fission products. Large tanks of water are located above the level of the reactor, and the passive coolant system provides enough water to keep the reactor core cool until a stable, controlled safe state is established. Additionally, the new systems are heavily computerized, contain many redundancies, and provide up-to-date displays to provide better data to operators.

Even though there is a lot of interest from the utilities in purchasing the new reactors, none have been ordered yet in the U.S., perhaps due primarily to the steep cost — several billion dollars per reactor. However, several utilities have obtained NRC approval of sites for new nuclear generating plants, and a few have made preliminary commitments to specific designs. The NRC has established a new division to handle applications for future reactors and expects to approve several for construction in the U.S. during the next decade.

How is nuclear waste handled?
Radioactive fuel that has undergone the usable amount of nuclear fission is removed from the reactor every one or two years and transferred to a used-fuel pool, where water keeps the fuel cool and provides shielding against radiation. The fuel is stored there for several years until it has a reduced level of heat and radioactivity. Next, the used fuel is placed in dry-cask storage, a stainless-steel vessel that is placed inside a concrete chamber and air cooled. Given that there is no national repository for nuclear waste — although the U.S. government promised to have one years ago — individual plants are building dry-cask storage facilities on their own sites.

The current administration in Washington has questioned whether we should consider reprocessing the used fuel, as is done in Europe. Reprocessing can separate the most radioactive and long-lived fission products and also enable uranium and plutonium fuel to be recovered for future use. The main issue with reprocessing is that it could lead to nuclear proliferation, which is why President Carter stopped it in the 1970s and why it remains unavailable in the U.S.

In decommissioned nuclear power plants, the spent fuel remains on the premises and is guarded and monitored continuously.

Have security measures changed?
Nuclear power plant security has always been a critical issue for the NRC, but the September 11 terrorist attacks prompted the agency to further tighten up its security requirements. Among the areas impacted by the NRC’s increased security rules are the requirement of watch towers at each plant, increased number of security guards and the types of weapons that they can use, increased number and height of fences surrounding the plants, and many different types of electronic security devices. In addition, more attention has been focused on the strength of the containment structure surrounding the reactor and its control and cooling systems. Originally, the containment structure was primarily used to keep things in, as in the Three Mile Island accident in which the reactor was severely damaged but very little radioactivity was released through the containment to the environment. But now the structure may also serve to keep things out, including airplanes.

What are NRC’s concerns about the future?
A significant concern at the NRC is the disappearing technical expertise in the field of nuclear energy. Most of the key technical work — understanding of materials within the reactors — was done in the 1960s and 1970s. The scientists and researchers who performed this work and wrote the regulations for reactors are retiring, so a huge knowledge base is disappearing. The nuclear engineering field is trying to recruit smart, interested individuals. One major manufacturer recently stated that it was looking for several thousand new nuclear engineers. Nuclear engineering departments in universities are presently undergoing a renaissance.

Another question is: who will be building the new reactors, since the U.S. has all but lost its manufacturing capabilities. Some key parts, such as the reactor vessel, will probably be made overseas, which may raise questions of quality assurance.

The NRC is also concerned with how to develop and apply regulations to new reactor designs that may use different fuels and cooling systems than the traditional light water-cooled reactors, which make up the present fleet of about 100 installed in power stations across the U.S. There has been an effort to make the regulations simpler and “technology neutral” so that the methods and evaluation criteria could be applied to any design, and the principles on which they are based would be more clearly understood by the public.

Professor Elsa Garmire:

WE NEED NUCLEAR POWER

The Sydney E. Junkins Professor of Engineering Sciences, Elsa Garmire is a member of the American Academy of Arts and Sciences and has been an advisor to the Department of Energy. She spent the past year as a Jefferson Science Fellow at the U. S. Department of State.

Where does nuclear power fit into the energy matrix?
There is no such thing as free energy. Every source has drawbacks and will harm the environment in some manner. Coal mining produces large amounts of greenhouse gases and acid rain and poses dangers to miners. Hydroelectric dams disrupt the natural environment for many types of wildlife. Renewable energy sources, such as wind and solar, can be unreliable given weather conditions. And as we haven’t yet developed good storage for renewables, we cannot depend on them at this time to meet all of our large-scale energy demands.

Over the next 50 years we will see a doubling of energy usage and a tripling of electrical usage. Unless patterns change dramatically, energy production and use will contribute to global warming through large-scale greenhouse gas emissions, with hundreds of billions of tons of carbon being emitted. Nuclear power provides the ability to help meet large-scale energy demands without producing carbon. Given this, I believe there is no way to plan for meeting future energy needs without nuclear power.

What are the advantages of nuclear energy?
Nuclear power is the most efficient energy source currently available. Uranium-235, the isotope used in nuclear reactors, can produce 3.7 million times as much energy as the same amount of coal. Uranium is abundant in several countries, including the U.S., South Africa, Australia, Canada, and Nigeria, and therefore is accessible. Nuclear energy also provides benefits beyond electricity generation. Radioactive materials, produced in reactors, are used in diagnostic and therapeutic treatments in medicine, weld inspection (radiography), power sources in remote locations and space applications, and food irradiation.

What about the negatives?
Fuel cycles that involve the chemical reprocessing of spent fuel to separate weapons-usable plutonium and uranium enrichment technologies are of special concern. New technologies are being suggested to recycle spent fuel in a manner that renders the material unsuitable for use in nuclear weapons, a huge advancement in safety.

Radioactive waste is a difficult issue. Although all spent fuel and its plutonium belong to the U.S. government, the U.S. does not have a long-term waste management system. In the 1960s and 1970s, utilities expected to send spent fuel to a reprocessing facility after a couple of years of storage in cooling pools on-site. President Carter restricted this option because of concerns about plutonium proliferation, and utilities have had to expand their storage space onsite.

There is no doubt that nuclear power is dangerous. The question is whether the huge benefits derived from nuclear power are worth the risks.

What are the challenges to expanding nuclear power production in this country?
The most significant challenge is the lack of innovation in nuclear technology since the 1960s. In the 1970s, fear of nuclear proliferation resulted in a turn against nuclear power. Fewer domestic institutions of higher education offered nuclear engineering programs, leading to a decline in research and new knowledge.

Other countries, such as France and Japan, have used nuclear power safely for decades, while the U.S. has lagged behind. To solve our energy needs, this country must undertake a complete rejuvenation of education and train a new generation of engineers in safe nuclear technology. We must also find a way to finance and regulate a next generation of safe nuclear power plants, not just build more of the same.

—Adrienne Mongan is a contributing editor at Dartmouth Engineer.

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Categories: Features

Tags: energy, environment, faculty

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